Unprocessed petroleum gas comprises a mixture of methane and heavier hydrocarbons such as ethane, propane, butane, etc, the actual composition varying according to the field from which it originates. For power stations and some industrial uses, unprocessed petroleum gas does not need processing, but for network distribution the gas is usually processed to bring its composition and calorific value within predetermined limits before supply to the distribution network.
Delivery of petroleum gas from an offshore field to a Processing station and/or distribution system onshore is not a problem for relatively large gas production fields for which it is economic to lay a delivery pipeline. For smaller fields and for the surplus gas obtained from oil production fields, however, it is not considered economic to provide for similar delivery of the gas, and the gas has so far not been used. In the case of oil field gas, it has been usual to burn off this gas at the production field, but in many areas such burning is now prohibited.
The present invention therefore aims to provide a method which will enable such gas to be delivered ashore in a sufficiently economic manner for it to be a practical proposition to make use of the gas. As an example, it has been estimated that, if it can be brought ashore economically, the surplus gas produced annually by the three oil fields in the Haltenbanken area of the Norwegian continental shelf, Njord, Draugen and Heidrun, would be sufficient to generate electricity equivalent to about 10% of the total electricity consumption of Norway in 1990.